Front Wheel Bearings

P

patrick flowers

New member
Sep 19, 1997
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Finally making some progress again. Got my rotors turned and mounted
back on the hubs, packed the bearings with Redline CV-2 and put the hubs
and knuckles back together last night.

While sitting there smugly admiring my work, I started thinking about
the design of this assembly. It then occurred to me that the only thing
holding the hub and bearings in the knuckle(other than the outboard seal
and retainer) is the interference fit between the knuckle and the outer
bearing races. Then I began to wonder if maybe the left side knuckle
slid over the bearings a little too easy...

Should I be concerned? I replaced the right side knuckle because of
obvious wear and abuse, but the left side "looked" fine. When I pulled
the left side knuckle down over the bearings with the Thoma tool, it
slid down in less than one second. When I did the left side, it took
about five seconds to pull it down. I guess I could keep a careful
watch on the space between the outer CV joint housing and the knuckle.
If the bearings start to "walk out", this space will get smaller with
the CV housing itself preventing any "automatic disassembly".

Not too late to order another knuckle...
Patrick
- --
Patrick Flowers
Mailto:patri63

The GMC Motorhome Page
http://www.gmcmotorhome.com
 
>
> Should I be concerned? I replaced the right side knuckle because of
> obvious wear and abuse, but the left side "looked" fine. When I pulled
> the left side knuckle down over the bearings with the Thoma tool, it
> slid down in less than one second. When I did the left side, it took
^^^^^^^
Oops! That should be "right" side. My GMC doesn't have two lefts.

> about five seconds to pull it down. I guess I could keep a careful
> watch on the space between the outer CV joint housing and the knuckle.
> If the bearings start to "walk out", this space will get smaller with
> the CV housing itself preventing any "automatic disassembly".

- --
Patrick Flowers
Mailto:patri63

The GMC Motorhome Page
http://www.gmcmotorhome.com
 
Patrick:

Why don't you contact Ken Thoma and then let us know what he says about
the fit and what the specs should be.

Paul Bartz

From: Patrick Flowers [mailto:patri63]
Sent: Tuesday, August 18, 1998 10:37 AM
Subject: GMC: Front Wheel Bearings

Finally making some progress again. Got my rotors turned and mounted
back on the hubs, packed the bearings with Redline CV-2 and put the hubs
and knuckles back together last night.
While sitting there smugly admiring my work, I started thinking about
the design of this assembly. It then occurred to me that the only thing
holding the hub and bearings in the knuckle (other than the outboard
seal and retainer) is the interference fit between the knuckle and the
outer bearing races. Then I began to wonder if maybe the left side
knuckle slid over the bearings a little too easy...
Should I be concerned? I replaced the right side knuckle because of
obvious wear and abuse, but the left side "looked" fine. When I pulled
the left side knuckle down over the bearings with the Thoma tool, it
slid down in less than one second. When I did the left side, it took
about five seconds to pull it down. I guess I could keep a careful
watch on the space between the outer CV joint housing and the knuckle.
If the bearings start to "walk out", this space will get smaller with
the CV housing itself preventing any "automatic disassembly".
Not too late to order another knuckle...
 
>
> Patrick:
>
> Why don't you contact Ken Thoma and then let us know what he says about
> the fit and what the specs should be.
>
> Paul Bartz

Good suggestion, although he might respond RTFM as he uses an inside
micrometer in the video to check the hub dimensions and IIRC he even
calls out the acceptable dimensions in the video. He's also quoted in
the GMCMI newsletters with the acceptable hub and knuckle dimensions.

I probably will pull down that side and find a local machinist with an
inside micrometer. Altho I think I already know the answer...

Patrick
- --
Patrick Flowers
Mailto:patri63

The GMC Motorhome Page
http://www.gmcmotorhome.com
 
Raceway fits, interference & non-interference are of concern. There should
be a tight fit of the raceway that is rotating. It is necessarily true that
both should have a tight or interference fit. One must know design
specifications. A bearing requires a specific clearence and/or abec fit.
These design criteria can be obtained from bearing manufactures, but,
bearing manufactures don't or may not know the bearings specific application
therefore they don't deal with application. I've made bearing clearence fit
calculation on machines having both rings rotating, both with interference
fits where around 0.0045" interference was required to obtain the 0.0015"
clearence. With a rotating inner ring on a car the tight fit comes from
basically zero ring to journal/shaft fit. The outter ring is rarely removed
for normal maintenance, so it has an interference fit and shouldn't spin in
its housing. The linear expansion of the bearing is nomally 6.25 x 10 to
the minus 6 pwr. I personally beleive in zero clearence cold setting for
wheel bearings as expansions open cleanence in this application. Using this
I've never had failure and when pulling the bearings for inspection as say
80 k miles they usually look good.

- -----Original Message-----
From: Patrick Flowers
To: gmcmotorhome
Date: Tuesday, August 18, 1998 10:58 AM
Subject: GMC: Front Wheel Bearings

>Finally making some progress again. Got my rotors turned and mounted
>back on the hubs, packed the bearings with Redline CV-2 and put the hubs
>and knuckles back together last night.
>
>While sitting there smugly admiring my work, I started thinking about
>the design of this assembly. It then occurred to me that the only thing
>holding the hub and bearings in the knuckle(other than the outboard seal
>and retainer) is the interference fit between the knuckle and the outer
>bearing races. Then I began to wonder if maybe the left side knuckle
>slid over the bearings a little too easy...
>
>Should I be concerned? I replaced the right side knuckle because of
>obvious wear and abuse, but the left side "looked" fine. When I pulled
>the left side knuckle down over the bearings with the Thoma tool, it
>slid down in less than one second. When I did the left side, it took
>about five seconds to pull it down. I guess I could keep a careful
>watch on the space between the outer CV joint housing and the knuckle.
>If the bearings start to "walk out", this space will get smaller with
>the CV housing itself preventing any "automatic disassembly".
>
>Not too late to order another knuckle...
>Patrick
>--
>Patrick Flowers
>Mailto:patri63
>
>The GMC Motorhome Page
>http://www.gmcmotorhome.com
>
 
patrick you have hit on a subject that I thought had been beat to death
before, but obviously we did not all come to closure on it. It is so
important that it does indeed deserve more discussion.

I will tell you what my position is and hopefully there will be lots of
discussion. I like the article done by cinnabar in GMC motorhome news june
1996, page 8.

If anyone is going to do the work on the front end themselves and especially
the hubs and bearings, I would strongly suggest that they not attempt it
without the proper tools. Sharing of tools is common in most of the GMC
motorhome clubs and is why I really think the clubs are great! At a
minimum you need a safe way to pull the hubs and remove and install the
bearings and a micrometer to check all tolerances. My reason for being so
tough on this part of the maintenance on our coaches is that the front hubs
and bearings are the weak point in the front end and a catastrophic failure
could lead to loss of control of the coach and a terrible accident. No one
needs that!

As to the hubs and bearings. Never replace the bearings and seals until you
have cleaned all surfaces, visually checked everything out checked all
tolerances with a micrometer.

When the hubs, bearings and knuckles are worked on they should be checked
for tolerances and mechanical integrity.

1. The hub should not have a step or taper in it, and should measure
2.0015" to 2.0020".If it is smaller than 2.0015" DO NOT USE IT, REPLACE IT.

2. Inspect the knucle for grooves and steps. Inside measurements are
3.2510" to 3.2525". In addition it should not be more than .0015' out of
round at any point. IF IT IS LESS THAN 3.2510" REPLACE IT. If it appears
damaged replace it. Alex Sirum has rebuilt ones that have been resleeved for
a little over $100.

3. When you have checked the tolerances first, and than installed the
correct bearings, you have done the best you can.

One last thing. And this will probably cause a fire storm! I noticed that
you had the rotors turned. I would not do it unless I had pulsating brakes
before I changed the bearings, or inspection of the rotors revealed a
physical problem. All it does is take metal off an already good surface.
Turning rotors has always been a good way for shops to make a little extra
money. If you replace the brake pads when they should be replaced and you
keep everything working right it is not necessary. All turning does is speed
up the replacement of the rotors.

Keep up the excellent questions thats how we all learn.

>Finally making some progress again. Got my rotors turned and mounted
>back on the hubs, packed the bearings with Redline CV-2 and put the hubs
>and knuckles back together last night.
>
>While sitting there smugly admiring my work, I started thinking about
>the design of this assembly. It then occurred to me that the only thing
>holding the hub and bearings in the knuckle(other than the outboard seal
>and retainer) is the interference fit between the knuckle and the outer
>bearing races. Then I began to wonder if maybe the left side knuckle
>slid over the bearings a little too easy...
>
>Should I be concerned? I replaced the right side knuckle because of
>obvious wear and abuse, but the left side "looked" fine. When I pulled
>the left side knuckle down over the bearings with the Thoma tool, it
>slid down in less than one second. When I did the left side, it took
>about five seconds to pull it down. I guess I could keep a careful
>watch on the space between the outer CV joint housing and the knuckle.
>If the bearings start to "walk out", this space will get smaller with
>the CV housing itself preventing any "automatic disassembly".
>
>Not too late to order another knuckle...
>Patrick
>--
>Patrick Flowers
>Mailto:patri63
>
>The GMC Motorhome Page
>http://www.gmcmotorhome.com
>
>
>
 
>
> patrick you have hit on a subject that I thought had been beat to death
> before, but obviously we did not all come to closure on it. It is so
> important that it does indeed deserve more discussion.

Sometimes I can be a slow learner.

> If anyone is going to do the work on the front end themselves and especially
> the hubs and bearings, I would strongly suggest that they not attempt it
> without the proper tools. Sharing of tools is common in most of the GMC
> motorhome clubs and is why I really think the clubs are great! At a
> minimum you need a safe way to pull the hubs and remove and install the
> bearings and a micrometer to check all tolerances. My reason for being so
> tough on this part of the maintenance on our coaches is that the front hubs
> and bearings are the weak point in the front end and a catastrophic failure
> could lead to loss of control of the coach and a terrible accident. No one
> needs that!

Guilty as charged. I agree completely. Actually, owning the mic's is
not really a necessity as it's pretty easy to find a machinist that can
mic the parts for you.


> Alex Sirum has rebuilt ones that have been resleeved for a little over $100.

Hubs and knuckles both for $125 each(ask me how I know)

> One last thing. And this will probably cause a fire storm! I noticed that
> you had the rotors turned.

Trust me, they needed it.

I guess the real reason for my post was my surprise at the realization
that the interference fit is the ONLY thing keeping the hub in its
proper place. With the axial clearance being so critical, it seems
absurd that there's no retainer provided. I knew the parts were
marginal, but until the above dawned on me, I didn't realize just how
dangerous this situation is. Makes me wonder if I shouldn't try to get
a set of Wallace hubs while there are still some available.

I'm not trying to cut corners, but at the rate I'm buying parts, I'm
beginning to wonder if I won't end up with Grandpa's Ax* here.

Patrick

*Granpa's Ax - It's had two new heads and three new handles, but it's
still a pretty good ax.
- --
Patrick Flowers
Mailto:patri63

The GMC Motorhome Page
http://www.gmcmotorhome.com
 
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